124 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



styles small or lacking, and large, low protocone with widely expanded 

 anterior and posterior cingula. 



Remarks. — Aside from its probable relationship to the Pantolestinae, 

 this group shows some resemblance to the Anisonchinae and to the 

 Apheliscidae, but in neither case is this resemblance close enough to 

 suggest real ajQanity. The enlargement of P^ and the general but 

 primitive stamp of the molars is not unlike the Anisonchinae but 

 does not include any detail such as might indicate a real relationship. 

 P*4 still more resemble those of Apheliscus but differ in cusp structure, 

 and the molars are widely different. It is not impossible that Aphelis- 

 cus is an offshoot of the same stock, but real evidence for such a hypoth- 

 esis is lacking. 



Genus APHRONORUS Simpson 



Aphronorus Simpson, 1935d, p. 230. 



Type. — Aphronorus fraudator Simpson. 



Distribution. — Middle Paleocene, Fort Union, Montana. 



Diagnosis. — Generally similar to Pentacodon. P4 with anterior end 

 less produced downward than in Pentacodon, talonid more distinctly 

 basined, with second cuspule more distinct. M2_3 less reduced 

 relatively to Mi. Trigonids of Mi_2 relatively shorter and entoconids 

 relatively higher than in Pentacodon. Three talonid cusps of M3 

 more distinct. P* with metacone well differentiated, protoconiile 

 distinct. M' and to less degree M^ slenderer and more transverse 

 than in Pentacodon, more leptictid in aspect. 



Remarks. — This genus is evidently closely allied to Pentacodon, and 

 its distinctive characters, taken together, do not definitely suggest 

 that it is necessarily either an earlier or a later stage in the Pentacodon 

 phylum. Evolution could have proceeded in either direction, or the 

 two may have diverged from a common ancestry. Nevertheless 

 Aphronorus does seem to resemble Palaeosinopa in more details than 

 does Pentacodon and to this extent may be supposed to retain more of 

 of the primitive characters of the family as a whole, despite its possible 

 divergence in other respects. 



APHRONORUS FRAUDATOR Simpson 



Figures 22-24 

 Aphronorus fraudator Simpson, 1935d, p. 230. 



T?/2?e.— U.S.N.M. no. 6177, left lower jaw with P4-M3. Collected 

 by A. C. Silberling. 



Horizon and locality. — Gidley and Silberling Quarries, Fort Union, 

 Middle Paleocene horizon. Crazy Mountain Field, Mont. 



Diagnosis. — Sole known species of genus. Dimensions given in 

 table 27. 



Remarks. — The lower canine, known from its alveolus only, is large 

 and semiprocumbent. Pi is very small and appears to have a single 



